1. Field of the Invention
The present invention pertains to towing vehicles, and more particularly to an apparatus that enables a first vehicle equipped with a drawbar to tow a second vehicle equipped with any of a variety of towing components.
2. Description of the Related Art
Various kinds of apparatus have been developed to tow trailers. A typical towing vehicle and trailer have complementary components that are engaged during a towing operation, and that are disengaged when the towing vehicle operates without a trailer.
Generally speaking, there are three major types of towing apparatus. The first type is called herein a simple receiver hitch. It comprises a receiver that is more or less permanently installed on the towing vehicle. The receiver is usually in the form of a longitudinally extending tube near the back end of the towing vehicle. One end of a shank is removably insertable into the receiver. A pin passing through the receiver and the shank retains the shank in the receiver. A second end of the shank protrudes from the receiver and is equipped with a hitch ball. The trailer has a cup, usually at the end of a tongue, that fits over the ball. A mechanism in the cup releasably locks the cup to the ball. Releasing the cup from the ball disengages the towing and trailers from each other. The strength of the entire simple receiver hitch system is limited by the strength of the pin and of the components that install the receiver to the trailer. Normally, the simple receiver hitch is limited to relatively small trailers, such as small boat and utility trailers.
Another type of towing apparatus is a pintle hitch, which is installed on a towing vehicle. A first kind of pintle hitch is comprised of a vertically oriented base with an upwardly oriented hook. Hinged to the base above the hook is a latch. The trailer has a tongue with an eye that fits over the hook. The latch is releasably lockable close to the hook tip to prevent the trailer eye from unintentionally disengaging from the hook. U.S. Pat. No. 5,332,250 teaches a typical hook kind of pintle hitch. Others are marketed by Northern Tool & Equipment Co. of Menomonee Falls, Wis.
A second kind of pintle hitch uses a hitch ball instead of a hook. The trailer may have an eye that engages the ball. The pintle hitch latch is lockable over the ball to prevent the trailer eye from unintentionally disengaging from the ball. Alternately, the trailer may be equipped with a cup that fits over and releasably locks to the ball. In that situation, the pintle hitch latch rests on but does not lock over the trailer cup. The latch therefore rubs and wears on the cup. U.S. Pat. No. 4,434,996 shows both the first and second kinds of pintle hitch.
The pintle hitch is generally considered to be stronger than the simple receiver hitch. However, a major problem with the pintle hitch is the difficulty in installing it to a towing vehicle. For maximum benefit of the pintle hitch, it is often fastened to a vertical surface of the towing vehicle frame. Doing so is not an easy task. Properly aligned holes must be drilled into the towing vehicle frame. Because the pintle hitch is heavy, it is difficult to hold in place while laying out the mounting holes. Even if a template is used, the installation process is cumbersome and time consuming. Further, there are significant safety concerns involved. The fasteners may be over-torqued or under-torqued. The fasteners may rust, thus both compromising their strength and making the pintle hitch difficult to remove. Drilling holes in the towing vehicle frame tends to weaken it. The overall capacity of the pintle hitch system is thus limited by the joint and fasteners between the pintle hitch and the towing vehicle.
In an attempt to ease the task of installing a pintle hitch to a towing vehicle, it is known to provide an adaptor that utilizes a receiver on the towing vehicle. The adaptor has a vertical mounting plate with pre-drilled holes to which the pintle hitch is fastened. The adaptor has a shank that is insertable into the receiver. A typical adaptor may be seen in the catalog of Northern Tool & Equipment Co. Although the adaptor simplifies the installation procedure, the entire system is limited in capacity by the strength and integrity of the fasteners between the receiver and the towing vehicle, by the fasteners between the pintle hitch and the adaptor, and by the pin between the receiver and the adaptor shank. In addition, it is known for the mounting plate to break, thus putting the trailer in the ditch.
U.S. Pat. No. 6,139,043 ('043 patent) describes a one-piece shank and pintle hitch. The shank is removeably insertable into a towing vehicle receiver. The one-piece hitch of the '043 patent eliminates the problem of a joint with fasteners between a pintle hitch and a vertical installation surface. Nevertheless, the capacity of the system is limited by the strength of the retaining pin between the shank and the towing vehicle receiver.
Other kinds of pintle hitches may be seen in U.S. Pat. Nos. 5,106,114 and 4,568,098.
The third major type of towing apparatus is a drawbar. Drawbars may be fixed to a towing vehicle, such as an agricultural tractor. Alternately, the drawbar may have limited motion relative to the towing vehicle, such as the drawbars of well know DMI bumpers. Drawbars are invariably horizontally oriented, and they have relatively large holes through them. A tow pin passes through the drawbar hole and a similar hole in a trailer tongue to engage the towed and towing vehicles. It is generally agreed that drawbars are the strongest and safest towing component for a towing vehicle. However, the tow pin and hole design for engaging a trailer is of rather limited usefulness. Versatility is an advantage of pintle hitches that is lacking in drawbars.
A major disadvantage of prior towing apparatus is related to the number of components that are required to suit different trailers. For the receiver type towing apparatus, one style of component is required for use with a hitch ball, while a different component is required for use with a pintle hitch. Thus, three different towing vehicle components are needed to suit just two types of towing apparatus. In fact, a third component is needed if a trailer is to be towed using a tow pin.
Thus, a need exists for improvement to towing apparatus.